by Ian Newton The massive declines in most farmland bird species that have occurred since the 1970s have not been conspicuously reversed in recent years, despite the wide uptake of agri-environment (AE) measures by farmers. This is the conclusion one would draw from the Breeding Bird Survey and other national monitoring schemes run by the BTO (Hayhow et al. 2016). But what about the situation at a more local scale? Three species â Corn Crake Crex crex, Stone-curlew Burhinus oedicnemus and Cirl Bunting Emberiza cirlus â have increased substantially following the application of AE measures designed specifically for them (Stanbury et al. 2010; Wotton et al. 2015; Hayhow et al. 2017). All three have restricted distributions within Britain, allowing most of their current geographical ranges to be targeted with AE measures, and all had been well researched beforehand. Other species have clearly benefited locally from measures specifically designed for them, including Grey Partridge Perdix perdix, Northern Lapwing Vanellus vanellus, Barn Owl Tyto alba and Corn Bunting E. calandra, the first two species chiefly where predator control was also imposed by the landowner (Merricks 2010; Perkins et al. 2011; Draycott 2012; Ewald et al. 2012; Setchfield et al. 2012; Norman 2013; Sotherton et al. 2014). Some seed-eating birds have also increased in association with the provision of wild-bird seed-crops or winter stubbles (Hinsley et al. 2010; Baker et al. 2012). However, apart from the three restricted-range species, increases at a local level have been insufficient to offset the overall national downward trend of most widespread farmland species. Other evidence on the effectiveness of AE measures has come from the bird populations on specific farms, which have increased markedly in response to measures intended to provide safe nesting habitat and year-round food, both for adults and for young. On the RSPBâs farm in Cambridgeshire, birds increased from 117 to 291 pairs over ten years (RSPB data); on the Game and Wildlife Conservation Trustâs farm in Leicestershire, birds increased from 749 to 1,437 pairs over 11 years (Stoate & Leake 2002), and at Titley Court Farm in Herefordshire from 531 to 951 pairs over just three years (Chapple et al. 2002). Increases of the same order have been recorded on many other large farms, most of which have been managed primarily for wild Grey Partridges, but on which other species benefited too. All the farms involved in these studies were run profitably from an agricultural viewpoint. Another three-year study also revealed that some bird species increased more, or declined less, on 65 farms under Higher Level AE management than on 21 farms lacking AE interventions (Bright et al. 2015). There can therefore be no doubt that, when carefully executed, AE measures have produced local increases in a wide range of priority bird species. The most likely reason why these species have not increased at the national level is that the critical AE measures have been applied over too small an area. Limited AE measures were first introduced in Britain in 1987, since when the areas eligible and variety of options available increased gradually, reaching their current format from 2005. However, at no time have AE measures been allocated more than 9% of the total agricultural subsidy budget; and the remaining 91% of this budget was spent on measures that could mostly be regarded as detrimental to birds. Similarly, while up to 70% of farms in recent years have taken up agri-environment measures, on most of these, AE measures affected only a small proportion (typically <5%) of the total farm area, mainly hedges and headlands. With such a small land area involved, we cannot expect birds to have recovered to anything like their 1970s abundance, although this is probably now an unrealistic target. Apart from too small an overall area, there may be other reasons why schemes have failed to produce an increase in bird numbers at national levels:
- Scientists may have diagnosed the causes of declines incorrectly, so that actions prescribed for population recovery were ineffective. In view of the increases in local areas, this seems unlikely.
- Not all farmers may have applied some measures to best effect. For example, grass mowing or hedge cutting at the wrong time of year can totally nullify any benefits that might otherwise accrue.
- Farmers may have selected as options things they were already doing or were easiest for them, rather than the ones that would give most benefit to local wildlife. Most farmers selected field boundary options, leaving the main parts of fields to be cropped intensively. Yet some species, such as Lapwing and Skylark Alauda arvensis, can be conserved only by in-field measures well away from boundaries. In addition, to increase numbers of some species, several measures need to be taken simultaneously. For example, Grey Partridges require adequate nesting cover, insects for chicks in summer, seeds for adults in winter, and some degree of predator control (Potts 2012). The lack of any one of these measures can prevent a population from increasing. Similarly, Lapwings in wet grassland require a high water table throughout the breeding season, little or no livestock grazing until after chicks are hatched, and no grass mowing until after chicks can fly. In some areas they also benefit from selective predator control. Again, failure to implement any one of these measures can prevent Lapwings producing enough young to maintain their numbers (Merricks 2010).
- Birds benefiting from measures on certain AE farms might then disperse elsewhere, so the benefits are spread over several farms, some of which may have no appropriate AE measures in place. Diluted in this way, the benefits may be too small to show on particular farms or in generally declining national populations.
- Particular measures of bird response may be inadequate. An example is when success is measured by the numbers of birds settling to breed and no account is taken of productivity, which may be too low to maintain numbers. Only longer-term monitoring would pick up a decline, so a scheme might be perceived as successful initially, but not in the longer term.
- Lack of potential colonists to re-occupy a newly restored habitat could be an increasing problem. Birds such as Grey Partridge and Corn Bunting are now so localised that they are unlikely to reach suitable areas more than a few kilometres from existing populations without deliberate translocation.
- Potentially the most useful AE scheme (AES), and on which most research was done, began in 2005, but it was followed in 2007 with the unexpected closure of set-aside. So some of the benefits derived from one scheme may have been offset by the loss of the other. Before its end, set-aside in England covered around 600,000 ha, perhaps 50â100 times more land than the equivalent uncropped habitat created under AE measures. The AES of the time was designed on the assumption that set-aside would still be in place, providing areas of in-field nesting and wintering habitat on most farms (Vickery et al. 2008).